Scientists have, for the first time, sent across quantum-secured message through the air above a city thereby demonstrating that practical quantum encryption over free-space networks is possible.

For those of you who are not aware with quantum encryption, it uses photons to encode information in the form of quantum bits. There are many forms of quantum encryption, but if we look at the simplest of all, which is known as 2D encryption, it involves each photon encoding one bit: either a one or a zero. There are high-dimensional forms of quantum encryption but practical implementation of these forms haven’t been possible until now.

Scientists have now been able to send messages in a secure manner using high-dimensional quantum encryption in realistic city conditions, including turbulence. Scientists are optimistic their work could potentially link Earth with satellites, securely connect places where it is too expensive to install fiber, or be used for encrypted communication with a moving object, such as an airplane. The study is published in journal Optica.

Scientists demonstrated 4D quantum encryption over a free-space optical network spanning two buildings 0.3 kilometers apart at the University of Ottawa. This high-dimensional encryption scheme is referred to as 4D because each photon encodes two bits of information, which provides the four possibilities of 01, 10, 00 or 11.

In addition to sending more information per photon, high-dimensional quantum encryption can also tolerate more signal-obscuring noise before the transmission becomes unsecure. Noise can arise from turbulent air, failed electronics, detectors that don’t work properly and from attempts to intercept the data.